1. Field of the Invention
The present invention relates in general to a seat belt retractor, and more particularly to a seat belt retractor with an electronically controlled tensionless mechanism.
2. Description of a Prior Art
Japanese Patent Application Second Provisional Publication No. 52-9891 shows a conventional seat belt retractor with a tensionless mechanism. In the known retractor, an electric motor is operated just after a seat occupant has worn a seat belt so as to rotate a belt take-up shaft in a belt feeding direction by a predetermined amount of slack. This known retractor, however, has a drawback that since the predetermined amount of slack is provided to the seat belt irrespective of the amount of an original slack which is held when the seat occupant has worn the belt, the resultant amount of slack may exceed an allowable amount if the original slack is large. This may obstruct the effective operation of the seat belt upon collision of a vehicle. Another drawback encountered in the known seat belt retractor is that since once the tensionless condition is established, the belt take-up shaft is locked and prevented from rotating in the belt feeding direction, the belt can not be pulled out of the retractor further, thus restraining the seat occupant from changing his or her sitting posture.